1 2 ...1 N 1K NCH IN H P H Ụ C K Ỳ T H I H Ọ C S IN H GI Ỏ I C Ấ P H A...

Bài 28:

¹

²

...1

ⁿ

1k n

CH IN H P H Ụ C K Ỳ T H I H Ọ C S IN H GI Ỏ I C Ấ P H AI

i

+ + + + + +  + − ≤ + − = + +k k k k k k... ... ...

( ) ( )

1

1

1

n

n

n

n n k k1 1 ... . 

n

1

 n n n= + ≤ < ⇒ = + ⇒ ≤ < + ⇒   =